src/Rel8/Table/Alternative.hs · rel8

on 28aaa76 help sign in

rel8/src/Rel8/Table/Alternative.hs

37 lines 1.1 kB history raw

1{-# language FlexibleContexts #-}

2{-# language StandaloneKindSignatures #-}

3{-# language TypeFamilies #-}

5module Rel8.Table.Alternative

6 ( AltTable ( (<|>:) )

7 , AlternativeTable ( emptyTable )

8 )

9where

11-- base

12import Data.Kind ( Constraint, Type )

13import Prelude ()

15-- rel8

16import Rel8.Expr ( Expr )

17import Rel8.Table ( Table )

20-- | Like 'Alt' in Haskell. This class is purely a Rel8 concept, and allows you

21-- to take a choice between two tables. See also 'AlternativeTable'.

23-- For example, using '<|>:' on 'MaybeTable' allows you to combine two tables

24-- and to return the first one that is a "just" MaybeTable.

25type AltTable :: (Type -> Type) -> Constraint

26class AltTable f where

27 -- | An associative binary operation on 'Table's.

28 (<|>:) :: Table Expr a => f a -> f a -> f a

29 infixl 3 <|>:

32-- | Like 'Alternative' in Haskell, some 'Table's form a monoid on applicative

33-- functors.

34type AlternativeTable :: (Type -> Type) -> Constraint

35class AltTable f => AlternativeTable f where

36 -- | The identity of '<|>:'.

37 emptyTable :: Table Expr a => f a